1. Field of the Invention
This invention relates to the manufacture of electronic modules, namely flip chip packaging, utilizing an improved method of assembling the module. The improved method provides enhanced adhesion between a chip and a substrate by treating the passivation coating of the chip. The result is a more robust electronic module.
2. Description of Related Art
Typically, in flip chip packaging, one or more integrated circuit chips are mounted on a substrate to comprise the electronic module. Pads on the chip are electrically and mechanically connected to corresponding pads on the substrate by a plurality of electrical connections such as solder joints. The chip and substrate are then subjected to a higher temperature causing the solder to melt and wet each pad in the module. The assembly is cooled causing the solder to solidify, thereby providing one or more electrical connections between the chip and the substrate to form the electronic module.
Subsequently, the module may receive a nonconductive underfill to reduce the fatigue of the solder joints, provide better adhesion between the chip and the substrate, and protect the module from contaminants. In underfilling the electronic module, a polymer, typically an epoxy resin, with ceramic or glass filler, is allowed to flow under the chip, between the solder joints, and heated at an elevated temperature to cure the underfill material.
However, it is difficult to promote adhesion between the chip and the underfill material. A layer of passivation on the chip once cured is substantially inert. Thus, it would be desirable to treat the cured passivation of the chip such that it is reactive and will bond to the underfill material.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a robust electronic module having enhanced adhesion between the chip and substrate.
It is another object of the present invention to provide a method of assembling a robust electronic module having enhanced adhesion between the chip and substrate.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a method for providing enhanced adhesion comprising the steps of:
(a) providing a polymeric film;
(b) modifying the polymeric film by oxidizing a surface of the polymeric film to form a modified polymeric film;
(c) treating the modified polymeric film with a polyamine;
(d) providing a polymeric material for adhesion to the polymeric film; and
(e) contacting the polymeric material to the polymeric film.
In another aspect, the present invention is directed to a method of forming an electronic module comprising the steps of:
(a) providing an integrated circuit chip having a passivation layer thereon;
(b) modifying the passivation layer by oxidizing a surface of the passivation layer forming a modified passivation layer;
(c) treating the modified passivation layer with a polyamine;
(d) providing a substrate;
(e) contacting the chip to the substrate;
(f) underfilling a gap between the chip and the substrate with an encapsulant; and
(g) curing the encapsulant.
Preferably, step (b) may comprise modifying the passivation layer with an O2 plasma at about 200 to about 400 Watts for about 0.2 to about 5 minutes at about 0.1 to about 1 Torr with an O2 flow rate of about 25 to about 200 cc/minute to form a modified passivation layer. Alternatively, step (b) may comprise modifying the passivation layer with ultraviolet light and O3 for about 1 to about 30 minutes at wavelengths of 184.9 nm and 253.7 nm to form a modified passivation layer. Preferably, step (c) comprises treating the modified passivation layer with a solution of about 0.1 to about 50 wt. % of a polyamine having a molecular weight of up to about 500,000.
Preferably, the polyamine comprises a cyclic amine having one of the following structures: 
wherein R may comprise a suitable alkyl group having the formula CxH2x-1, where X is from 1 to 10 and n is about 90 to about 5000.
In yet another aspect, the present invention is directed to a method of forming an electronic module comprising the steps of:
(a) providing an integrated circuit chip having a polyimide layer thereon, a surface of the polyimide layer modified to form a modified polyimide layer;
(b) treating the modified polyimide layer with a 1 to 5% solution of poly(4-vinylpyridine);
(c) providing a substrate having interconnect pads corresponding to solder joints on the chip;
(d) contacting the chip to the substrate;
(e) forming an electronic module by reflowing the solder joints to electrically and mechanically connect the chip to the substrate;
(f) underfilling the electronic module with an encapsulant; and
(g) curing the encapsulant for a sufficient time and temperature.
Preferably, step (b) comprises treating the modified polyimide layer with an about 5% solution of poly(4-vinylpyridine) at about 0xc2x0 C. for about 5 minutes such that the poly(4-vinylpyridine) substantially coats the modified polyimide layer. Preferably, during reflowing of the solder joints in step (e), the poly(4-vinylpyridine) substantially reacts with the modified polyimide layer.
In still yet another aspect, the present invention is directed to a method of treating a wafer to provide chips having enhanced adhesion in an electronic module comprising the steps of:
(a) providing a wafer having a plurality of electrical devices formed and a passivation layer thereon;
(b) patterning and etching the passivation layer to form bonding pads corresponding to the electrical devices;
(c) applying solder to the bonding pads;
(d) oxidizing a surface of the passivation layer to form a modified passivation layer;
(e) treating the modified passivation layer with a solution of about 0.1 to about 50 wt. % of a polyamine;
(f) reflowing the solder; and
(g) dicing the wafer to form individual chips.
Preferably, the polyamine comprises a cyclic amine having one of the following structures: 
wherein R may comprise a suitable alkyl group having the formula CxH2x-1, where X is from 1 to 10 and n is about 90 to about 5000. Most preferably, the polyamine comprises poly(4-vinylpyridine) having a molecular weight of about 20,000.
In a final aspect, the present invention is directed to an electronic module comprising a substrate; an integrated circuit chip aligned to the substrate through a plurality of solder joints, the chip having a layer of passivation thereon, the layer of passivation having an oxidized surface and treated with a polyamine; and an underfill material disposed between the chip and the substrate, wherein upon heating the module to reflow the solder joints, the oxidized surface of said passivation is adapted to react with said polyamine, and during curing of said underfill material, said underfill material is adapted to react with said polyamine.
Preferably, the polyamine comprises poly(4-vinylpyridine).